Annals of Botany 118: 259–270, 2016 doi:10.1093/aob/mcw104, available online at www.aob.oxfordjournals.org Specific peroxidases differentiate Brachypodium distachyon accessions and are associated with drought tolerance traits Na Luo1, Xiaoqing Yu2, Gang Nie3, Jianxiu Liu4,* and Yiwei Jiang5,* 1College of Life Sciences, South China Agricultural University, Guangzhou 510642, China, 2Department of Agronomy, Iowa State University, Ames IA 50011, USA, 3Department of Grassland Science, Sichuan Agricultural University, Chengdu 611130, 4 5 China, Institute of Botany, Jiangsu Province & Chinese Academy of Science, Nanjing 210014, China and Department of Downloaded from https://academic.oup.com/aob/article/118/2/259/1741503 by guest on 27 September 2021 Agronomy, Purdue University, West Lafayette, IN 47907, USA *For correspondence. E-mail [email protected] or [email protected] Received: 14 November 2015 Returned for revision: 8 February 2016 Accepted: 4 April 2016 Published electronically: 20 June 2016 Background and Aims Brachypodium distachyon (Brachypodium) is a model system for studying cereal, bioen- ergy, forage and turf grasses. The genetic and evolutionary basis of the adaptation of this wild grass species to drought stress is largely unknown. Peroxidase (POD) may play a role in plant drought tolerance, but whether the al- lelic variations of genes encoding the specific POD isoenzymes are associated with plant response to drought stress is not well understood. The objectives of this study were to examine natural variation of POD isoenzyme patterns, to identify nucleotide diversity of POD genes and to relate the allelic variation of genes to drought tolerance traits of diverse Brachypodium accessions. Methods Whole-plant drought tolerance and POD activity were examined in contrasting ecotypes. Non- denaturing PAGE and liquid chromatography–mass spectrometry were performed to detect distinct isozymes of POD in 34 accessions. Single nucleotide polymorphisms (SNPs) were identified by comparing DNA sequences of these accessions. Associations of POD genes encoding specific POD isoenzymes with drought tolerance traits were analysed using TASSEL software. Key Results Variations of POD isoenzymes were found among accessions with contrasting drought tolerance, while the most tolerant and susceptible accessions each had their own unique POD isoenzyme band. Eight POD genes were identified and a total of 90 SNPs were found among these genes across 34 accessions. After controlling population structure, significant associations of Bradi3g41340.1 and Bradi1g26870.1 with leaf water content or leaf wilting were identified. Conclusions Brachypodium ecotypes have distinct specific POD isozymes. This may contribute to natural varia- tions of drought tolerance of this species. The role of specific POD genes in differentiating Brachypodium acces- sions with contrasting drought tolerance could be associated with the general fitness of Brachypodium during evolution. Key words: Brachypodium distachyon, drought tolerance, gene and trait association, natural variation, peroxidase, single nucleotide polymorphism. INTRODUCTION et al.,2012; Thole et al., 2012) and genome diversity (Gordon et al., 2014). All these tools and resources are valuable for ex- Brachypodium distachyon (Brachypodium) is a temperate, amining the genetic and evolutionary basis of complex traits monocot wild grass species and it possesses all the qualities to such as abiotic stress tolerance. make it an excellent model organism (Garvin et al.,2008; Antioxidant metabolism plays a role in drought tolerance of Bevan et al.,2010). It has diploid ecotypes containing five the plants. As one of the reactive oxygen species, hydrogen per- chromosomes, easily distinguishable chromosomes (2n ¼ 10), oxide (H2O2) is a by-product of biological reactions in the plant small genome size (approx. 300 Mbp), self-fertility, small phys- cell. Adverse environmental conditions such as drought stress ical status, short life cycle and a simple growth requirement can promote excess accumulation of H2O2, potentially leading (Draper et al., 2001). This species is phylogenetically closer to to oxidative damage to protein, DNA and lipids (Apel and Hirt, some economically important food and bioenergy crops than is 2004).Thedegreeoflipidperoxidation, indicated by the level rice (Oryza sativa)(Draper et al., 2001), thus providing a pow- of malondialdehyde (MDA) content, often increased under erful tool for studying functional and ecological genomics drought stress in plant species (Zhang and Kirkham, 1996; Jiang aimed at improving grain, forage and bioenergy crops. To date, et al., 2010; Xu et al.,2011; Liu and Jiang, 2015). Removal of genetic and genomic resources for Brachypodium have been de- H2O2 is accomplished by the action of several antioxidant en- veloped, including the entire genomic sequence (Vogel et al., zymes at different cellular locations. Of the antioxidative en- 2010), a genetic linkage map (Garvin et al., 2010), a high- zymes, peroxidase (POD) catalyses the reduction of H2O2 to efficiency transformation system (Vogel et al.,2006; P~acurar water, followed by subsequent oxidation of small molecules et al.,2008; Vogel and Hill, 2008), T-DNA mutants (Bragg (Smith and Veitch, 1998). Drought stress often induces POD VC The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: [email protected] 260 Luo et al.—Brachypodium peroxidase and drought tolerance activity in many plant species (Jung, 2004; Sofo et al., 2005; Natural populations are often collected from a wide range of Upadhyaya et al., 2008; Selote and Khanna-Chopra, 2010; Ying geographical locations that have enormous diversity, which can et al.,2015). The tolerant genotype of maize (Zea mays)ex- maximize the potential of populations to withstand and adapt to hibited lower accumulation of MDA and H2O2 content related biotic and abiotic environmental changes (Jump et al.,2009). to increasing activities of POD and other antioxidant enzymes Natural Brachypodium accessions broadly group into winter under water stress conditions (Moussa and Abdel-Aziz, 2008). and spring annuals, and this may impact plant responses to en- Increases in POD activities were also found at the vegetative vironments. Luo et al. (2011) found that 57 Brachypodium nat- and flowering stages of seven species within the genus Avena ural accessions varied considerably in whole-plant responses to under drought stress, coupled with an increased level of lipid drought stress and they were classified into most tolerant, mod- peroxidation (Pandey et al.,2010). However, POD activity also erately tolerant, susceptible and most susceptible groups. remained unchanged in some annual and perennial grass species Comparative analysis of the cold acclimation and freezing tol- exposedtodroughtstress(Zhang and Kirkham, 1996; Zhang erance capacities of seven diploid Brachypodium accessions re- Downloaded from https://academic.oup.com/aob/article/118/2/259/1741503 by guest on 27 September 2021 and Schmidt, 1999; Fu and Huang, 2001; Bian and Jiang, 2009; vealed only a limited capacity to develop freezing tolerance Jiang et al., 2010). Although two cultivars of Kentucky blue- when compared with winter varieties of temperate cereals such grass (Poa pratensis) did not differ in POD activities under as wheat (Triticum aestivum)andbarley(Colton-Gagnon et al., drought stress, the drought-tolerant cultivar exhibited signifi- 2014). In addition to stress tolerance, Schwartz et al. (2010) re- cantly higher POD activities compared with the sensitive one af- ported that VRN (vernalization regulator) and a portion of the ter rewatering (Xu et al., 2011). The results demonstrated phenotypic variation of flowering time and vernalization was complex responses of POD to drought stress, influenced by plant associated with changes in expression of orthologues of VRN species, cultivar, stress intensity and duration. genes in Brachypodium accessions. Variation of phenotypic In spite of their role in detoxification, PODs have remarkable traits such as plant height, growth habit, stem density, flowering catalytic versatility involved in a broad range of physiological time, seed weight and cell wall composition were also observed and developmental processes, including initiation of seed ger- amonginbredlines(Tyler et al., 2014). Natural populations of mination (Morohashi, 2002), cellular growth and cell wall loos- Brachypodium exhibit distant genetic distance patterns (Vogel ening (Cosgrove, 2001), cell wall cross-linking (Passardi et al., et al.,2009); however, the mechanisms of environmental 2004b), lignification and suberization (Lopez-Serrano et al., adaptation during evolution are not well understood in 2004), differentiation (Kim et al., 2004), senescence (Ranieri Brachypodium. For example, it is not well understood whether et al., 2000) and plant–pathogen and plant–insect interactions some candidate genes encoding POD contribute to variable (Delannoy et al., 2003; Gulsen et al., 2010a). Existing as isoen- drought responses of natural accessions. zymes in plant species, the class III plant POD is a haem- Although it can be challenging to determine the functions of containing glycoprotein encoded by a large number of super- a large number of isoenzymes in a single plant species, accumu- family genes in land plants (Welinder, 1992a, b; Hiraga et al., lation of information on individual genes should lead to a better